1. Field of the Invention
The present invention relates to a projector, and more particularly to a projector using LEDs as light sources.
2. Description of the Related Art
FIG. 1 shows a schematic view of a conventional projector. The projector 1 includes a white lamp 11, a condenser lens 12, a color wheel 13, an integrator rod 14, a relay lens 15, a total internal reflection prism 16, a digital micromirror device (DMD) 17, and a projection lens 18.
The white lamp 11 is employed for generating white light. The white light is accommodated by the condenser lens 12, and passes through the color wheel 13 having red, green, and blue (RGB) color zones, so as to generate consecutive and fast alternating RGB color fields. Next, the light passes through the integrator rod 14 and the relay lens 15 for uniformity. The uniform light then passes through the total internal reflection prism 16, and is reflected by the total internal reflection prism 16 to the DMD 17. Finally, the light is reflected by the DMD 17, passes through the total internal reflection prism 16, and enters the projection lens 18. The projection lens 18 projects the light onto a projection plane area (not shown).
In the projector 1, the white lamp 11 may be a tungsten-halogen lamp or a high-intensity discharge lamp (HID lamp). The tungsten-halogen lamp is unable to generate a high luminance. The HID lamp includes a xenon lamp, a metal-halide lamp, and an ultra-high-pressure (UHP) mercury lamp. The xenon lamp is advantageous in having a flat spectrum in the visible light range, desirable color temperature (about 6000 k), short warm-up time, and perfect chromatic value, but disadvantageous in having a low light-emitting efficiency, short service life, high price, and generation of excessive heat during operation.
The metal-halide lamp achieves a higher light-emitting efficiency (about 65 to 75 lumens/watt) and has a perfect chromatic value, but is disadvantageous in having a long arc, excessively long warm-up time, short service life, generation of various colors by the arc at different positions, and generation of a large amount of heat. The UHP mercury lamp has a short arc, long service life, and high light-emitting efficiency, but is rather expensive and unsafe in use due to its potential explosion hazard.
Moreover, since the projector 1 uses the white lamp 11 as its light source, the color wheel 13 is adopted to control the color, and a motor is required to drive the color wheel 13. Therefore, the projector 1 has too many elements, and the volume of the projector 1 becomes too large. Besides, two-thirds of the light flux is lost when the light passes through the color wheel 13.
Therefore, it is necessary to provide a projector using LEDs as light sources to solve the above problems, minimize volumetric size and promote light efficiency of projectors.